Thermal overload release device for automatic circuit breakers



Sept. 26, 1951) E. BESAG ET AL 2,523,897

- THERMAL OVERLOAD RELEASE DEVICE FOR AUTOMATIC CIRCUIT BREAKERS Filed Aug. 4, 1948 2 SheetsSheet 1 MUM!! M .n

Attorneys,

Sept. 26, 1950 E. BESAG ETAL 27,523,397

THERMAL OVERLQAD RELEASE DEVICE FOR AUTOMATIC CIRCUIT BREAKERS Filed Aug. 4, 1948 2 sheets-sheet 2 F/G 2. n 0/ Z s p w m 2 r l l l l: l\ I I" I I H /b 9 II F s P 12 Attorneys,

Patented Sept. 26, 1950 THERMAL OVERLOAD RELEASE DEVIQE FOR AUTOMATIC CIRCUIT BREAKERS Ernst Besag and Walter Edward Hill, Streetly,

and Thomas Daniel Guy Wintle, Walsall, England, assignors to J. A. Crabtree & Co. Limited, Walsall, England, a British company Application August 4, 1948, Serial No. 42,494 In Great Britain August 14, 1947 Claims.

This invention relates to improvements in thermal overload release devices for automatic circuit breakers, and is particularly concerned with protective switches adapted to be tripped by bimetal thermal devices in the event of overload.

The principal object or the invention is to provide an improved arrangement of compact con struction adapted for providing a prolonged time lag before tripping operation on overload, while enabling quick re-setting after a tripping operation.

According to one feature of the present invention, a bimetal element of partly cylindrical form is disposed on a vertical axis around a heater coil and former. The disposition of the parts in this manner improves the space factor and provides a very compact construction. The ends of the bimetal may each be engaged with one member of a differential trip mechanism.

According to a further feature of the invention, the former, on the centre axis of which the bimetal is mounted, is made of metal, for providing a heat reservoir giving a long time lag. The production of this member from metal also enables it to be simply produced to close limits, whereby the drilled hole for receiving the pivot pin of the bimetal member can be accurately positioned.

According to a still further feature of the invention, we provide an overload box, having vertical partitions to form chambers, each of which chambers receives a thermal device therein and has a floor or bottom positioned in spaced relation above the underlying parts of the circuit breaker so that the heater devices above the floor or bottom are heat-insulated from the conductors and coil terminations disposed below said floor or bottom.

In order to enable the invention to be readily understood, reference will now be made to the accompanying drawings illustrating, by way of example, one construction for carrying the invention into effect, in which drawings Figure l is a plan of an overload box, parts of which are broken away to disclose the construction more clearly.

Figure 2 is a section on the line II-II of Figure 1.

Figure 3 is a perspective view of a bimetal element.

Figure 4 is a perspective view of a bimetal element with the parts disassembled.

Figure 5 is a perspective view of a heater element mounted in its chamber and showing also parts of the trip bar.

Referring to the drawings, an overload box a made ofxinsulating material is partitioned to provide along the rear of the box a long narrow compartment b for the reception of trip bars cd. Two end compartments 6 are provided and accommodate, respectively, the ambient compensating means g and the trip mechanism h. Between these two end compartments, three intermediate chambers lc are formed, each chamber containing therein a thermal release unit m. The overload box a is also provided with three pockets 11 open at the front of the box and having the rear wall thereof spaced horizontally in front of the front walls of the intermediate chambers k, the space between said walls communicating with the space below the floor or bottom of the chambers Is. The three pockets n are provided for the reception therein of terminals 00 Each pocket n is divided horizontally by a partition, the space above which partition houses the contacts 00 while the space below the partition provides arc chambers for fixed contacts 8.

Each thermal unit has a vertically arranged metal'former p secured by rivet ng 1 to the bottom of a chamber k. Around this metal former is disposed a heater coil 3, which in turn is enclosed by a bimetal strip t. This bimetal strip is bent to almost a complete cylinder, one end having a flat extension 15 disposed between a lateral abutment c on the trip bar 0 and the casing at u, while the other end is secured to a V-shape metal lever 12. One leg 12 of this lever is bent at right angles for riveted attachment to the bimetal t, the end of the other leg 0 being engaged with the trip bar d. At the apex of the lever 12, is a pin to extending centrally of the bimetal strip 15 into an axial hole drilled in the metal former p so as to be rotatable therein.

The lower end of the heater coils s is Welded to a terminal as on the bottom of the box, and the upper end is bent downwardly to form a leg s disposed outside the coiled portion in the gap t of the bimetal strip t and havin its ends connected by welding with a second terminal 3: The coil s is insulated from the metal former by the provision around the latter of a sleeve y of asbestos or glass fibre or of a coating of vitreous enamel.

Mica shields I, 2 are provided on each end of the heater coil s for localizing heat from said coil and directing it on to the bimetal strip t, and also for preventing convection currents which would cause heat dispersal. The lower end of the metal former seats on the shield or disc 2, while its upper end has a central raised portion p affording a reduced bearing area for seating the pin 10. The top cover 3 of the box is formed with recesses which are partly filled with an asbestos shield or plate 4 which, together with the resultant air gaps 5, further reduce heat losses.

The rear chamber b not only affords space for accommodating the trip bars cd, but also constitutes still-air spaces for preventing heat dissipation. Spaces 5 in front of the heater chambers constitute funnels for producing a cooling efiect between each chamber and a main terminal 0. Through this space passes the connecting strip 5 between the terminal a: of a heater coil and the main terminal 0 and also a further strip 1 which connects the terminal 1: of the heater coil and the main fixed contact 8 with a second terminal 0 which may be employed for feeding another contactor or contactors from the same overload unit. A moving contact 9 for coperating with fixed contacts is shown in Figure 2.

The main fixed contacts 8 at the front of the box are each connected by a strap ill to the terminal x of the heater coils. The contacts 8 are disposed in arc chambers contained within the width of the box, and each terminal 0 is separated from its contact 8 by an inclined surface of the box constituting an arc shield l I The box is constructed so that the heater chambers are closed except for openings through which extend the ends of the bimetal t for actuating the trip bars cd, these openings being small and as remote from each other as possible, for reducing the heat losses from individual chambers. It will be noted that the box has a floor or bottom l2 so that the heater devices above it are insulated from the conductors 6, ID and the coil terminations arw disposed in the space below said floor or bottom.

We claim:

1. A relatively shallow overload box for an automatic circuit breaker comprising a substantially rectangular box-like casing; a vertically disposed partition spaced inwardly from the rear wall of said casing to provide a chamber extending along the rear of said casing, said partition having a plurality of spaced openings therein; a trip bar within said rear chamber and extending along the length thereof; a plurality of vertical partitions within said casing disposed in a direction normal to that of the partition defining the rear chamber to provide a plurality of intermediate chambers; a thermal overload release device within each intermediate chamber, each of said devices having a bimetallic element disposed in a vertical axis with an arm extending through one of the openings in the partition at the rear of the casing and engaging the trip bar; a plurality of vertical partitions within said casing at the front thereof and extending in a direction substantially parallel to the partitions defining the interemediate chambers, to provide a plurality of front chambers; a terminal for the heater coil of one of said thermal release devices within each of said front chambers; and a fixed contact for the circuit breaker on which said overload box is mounted within each of said front chambers.

2. A relatively shallow overload box as defined in claim 1 and including a chamber extending along one side of the casing, and an ambient compensating mechanism within said chamber.

3. A relatively shallow overload box as defined in claim 1 and including a chamber extending along one side of the casing, and a circuit breaker trip mechanism Within said chamber and adapted for actuation by the trip bar in the rear compartment of said casing.

4. A relatively shallow overload box as defined in claim 1 including a chamber extending along one side of the casing, an ambient compensating mechanism within said chamber, a chamber extending along the opposite side of the casing, and a circuit breaker trip mechanism within said last mentioned chamber adapted for actuation by the trip bar in the rear compartment of said casing.

5. A relatively shallow overload box as defined in claim 1, in which the front chambers are spaced in front of the intermediate chambers to provide a space therebetween for the circulation of air.

ERNST BESAG. WALTER EDWARD HILL. THOMAS DANIEL GUY VVINTLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Besag Feb. 4, 1936 FOREIGN PATENTS Number Number 

